On your travels, three men stand at a fork in the road. You're not sure which fork you need to take, but each of the three men do. One of these people tells the truth, one always lies, and the third tells the truth sometimes and lies the other times. Each of the three men know each of the others, but you don't know who is who. If you could ask only one of the men (chosen at random, since you don't know which man is which) one yes/no question, what question would you ask to determine the road you wish to take?

The question is too vague. If the third man may answer randomly, then it's not possible to determine the correct route with only a single question. If the third man always answers a question either entirely truthfully or entirely untruthfully (but may change behavior when the question is changed or repeated), then it is possible to determine the correct route with a single question.

You have to be more specific about how exactly the third man may behave.